The Independent disclosed leaked Whitehall correspondence yesterday showing that the Prime Minister and senior Cabinet ministers quashed a plan by the Secretary of State for National Heritage, Peter Brooke, to act on the Jenkins Committee report and free this important London vista of parked cars.
A senior source also revealed that civil servants who park on Horse Guards Parade had urged ministers to block the proposal.
Taking parked cars off Horse Guards Parade has also been a target of the Independent's campaign to improve the spaces around key historic and cultural buildings.
Last night, Dame Jennifer said: 'We stick totally to our recommendations. The Government say they are still under review and I still hope they will proceed. It is clear that there are a number of issues that have become entangled.
'The fact that Horse Guards Parade is where civil servants park their cars does appear to be of particular relevance here. Civil service parking would seem to have policy implications.'
She added that her committee had looked into who parks on Horse Guards Parade and she was 'in no doubt that nearly all those who did could park near by or use public transport'.
The Department of National Heritage maintained that despite the revelations of the letters, ministers at the department still intended to pursue the Jenkins recommendations, and the chief executive of the Royal Parks Agency, David Welch, would be holding discussions with government ministries.
A Downing Street spokeswoman would make no comment. But she pointed out that the leaked letter stated it would be inappropriate to review the position 'at present'.
John Gummer, the Minister for London, is understood privately to be in favour of the call for cars to be removed from Horse Guards Parade, but remains opposed to the closure of Horse Guards Road. A spokesman said yesterday: 'His opposition is based on the fact that if you shut the road to traffic you cause congestion in Parliament Square.'
When told that Mr Gummer's reasoning - that alternative routes between SW1 and W1 were longer - was incorrect according to an Independent test run, the spokesman said that 'the minister's view remained unchanged'.
A spokesman for Michael Howard, the Home Secretary, who also wrote confidentially to the heritage department to block the initiative, said: 'We don't comment on leaked documents.
'And we don't comment on terrorist and security aspects, which were among the areas of concern that Michael Howard set out.'